Creating the illusion of three-dimensional (3D) images on a display device or projection screen has been attempted for many years. In the 1950s, 3D movies were popular with polarized glasses worn to separate images for the left and right eye to provide for a stereoscopic view of the movie. Another area in which 3D imagery has been attempted is on raster scan displays. Generally, when the term 3D is used in regard to computer graphics, the term is referring to planar generated 3D images that are created using geometric perspective and projection transformations and other monocular depth cues such as hidden line removal, surface modeling, shading, texture mapping, and rotation. These techniques are appropriate for computer games and CAD application software but only provide the illusion of a 3D display because the scene is shown on a 2D display.
Stereoscopic images present the viewer with slightly different perspectives for the left and right eyes which fuse together to provide a sense of depth, in a process called stereopsis. Stereoscopic displays typically require the use of some device worn by the viewer to separate the left and right eye perspectives. Autostereoscopic displays make use of some device externally attached to the 3D display to generate the left and right views without the aid of a special viewing aid worn by the viewer. Again, this technology only provides the illusion of a 3D display because the scene is still shown on a 2D display.
A true 3D display would have two qualities: First, a true 3D display would allow several observers looking at the same scene to simultaneously see different parts of the objects in the scene and may even see somewhat different sets of objects. An additional property of such a real 3D scene is that an observer with two eyes will see slightly different views of the scene from each eye, and the brain will use these differences to create a perception of the distance between the objects and the observer. Second, a true 3D display would allow the observer to move around the display and view the scene from any position, including the front, back, top, bottom, and any of the sides. In this regard, a true 3D display would be 3D.